This study is a monocenter study investigating the effects of 3% diclofenac in 2.5% hyaluronic acid gel on tumor metabolism in the treatment of actinic keratoses. Treatment duration is 3 months. Skin biopsies will be obtained before treatment, at the end of the treatment and four weeks after the treatment. Control biopsies at visit 1 and 3 are performed in healthy, sun damaged and untreated skin. Evaluation of efficacy will be performed at the end of the treatment and four weeks after the treatment.